1. Field of the Invention
The present invention relates to a method of adding crystallization promoting catalyst elements to a semiconductor material partially or entirely consisting of an amorphous component, or a substantially intrinsic polycrystal semiconductor material, subjecting the semiconductor material to an annealing process or the like, to thereby improve the crystallinity of the semiconductor material, and further efficiently moving the crystallization promoting catalyst elements to a region where the semiconductor device is not adversely affected by the crystallization promoting catalyst elements.
2. Description of the Related Art
In recent years, a research on a technique of lowering a temperature during a semiconductor device process has been extensively advanced. The main reason is because the semiconductor device needs to be formed on an insulating substrate made of glass or the like which is inexpensive and rich in processability.
A melting point of glass widely and generally used as the substrate of a semiconductor film is about 600xc2x0 C., and the temperature of the substrate cannot be made higher than 600xc2x0 C. Therefore, the semiconductor device must be manufactured at a temperature lower than about 600xc2x0 C.
In the semiconductor process, there may be required that the amorphous component contained in the semiconductor material or an amorphous semiconductor material is crystallized, or that the crystallinity is improved.
Up to now, thermal annealing has been made to satisfy the above requirements. In the case where silicon is used as the semiconductor material, annealing is conducted at a temperature of 600 to 1100xc2x0 C. for 0.1 to 48 hours or more hours, to thereby crystallize the amorphous material, to improve the crystallinity and so on. When the thermal annealing is intended to be thus conducted on a semiconductor film formed on a glass substrate, since the crystallinity must be improved at a temperature extremely close to a strain point of the glass substrate, that is, at about 600xc2x0 C., a very long time is required for crystallization. The temperature of 600xc2x0 C. is close to the lowest temperature required for the crystallization of silicon, and when the temperature is 500xc2x0 C. or lower, no crystallization occurs even if annealing is continued for a long period of time.
Therefore, there is required that the conventional crystallizing process is reconsidered from the viewpoint of making the process temperature low. The laser beam irradiation technique is one of techniques that realize a low-temperature process. This is because a laser beam can give a high energy equal to thermal annealing at about 1000xc2x0 C. restrictively to only a semiconductor film so that the entire substrate does not need to be exposed to a high temperature. The irradiation of a laser beam is mainly made by a method in which a large-energy laser pulse is irradiated onto the semiconductor material using a pulse oscillation laser such as an excimer laser so that the semiconductor material is instantaneously melted and solidified, to thereby crystallize the semiconductor material. The crystallinity of the semiconductor film obtained by crystallization due to the laser of this type is relatively high.
However, the characteristic of a TFT manufactured using a silicon film thus crystallized by the laser is varied by instability of the laser, which requires further review.
Under the above circumstances, the present inventors have devised a method in which nickel which is one of elements that promote the crystallization is added to amorphous Si deposited through the plasma CVD method, and thermal annealing is then conducted on the amorphous Si to make the amorphous Si grow in a solid layer. This method enables the amorphous Si to be changed into a polycrystal Si film under a low-temperature and short-period condition, that is, at 600xc2x0 C. for 4 hours.
The above method using nickel enables the polycrystal Si film to be formed on the glass substrate without using the laser for a relatively short period of time. However, disappointedly, the characteristic of the polycrystal Si film is not satisfactory in comparison with a film obtained through the laser. Concentrations of nickel are found everywhere in the interior of the film obtained by the above method in which nickel is added to the amorphous Si. When a portion where nickel is concentrated is unexpectedly in a channel region or a high-resistant region (for example, a portion called xe2x80x9coffset regionxe2x80x9d) of the TFT, the characteristic is significantly degraded. In particular, an off-state current is remarkably increased.
From the above viewpoints, the present inventors reviewed a method of removing nickel from a film in which nickel is contained, or reviewed a method of removing nickel from at least the channel region and the high-resistant region. Then, the present inventors have paid attention to a phenomenon in which annealing is conducted on a nickel contained film to which phosphorous is selectively added, to thereby allow nickel to be attracted to phosphorus so that nickel is substantially removed from a region other than a region where phosphorus is added, and tried to optimize the condition of the phenomenon. A technique of removably sucking the impurities is generally called xe2x80x9cgetteringxe2x80x9d.
The above method is usually that, typically, after phosphorus is added to the film, thermal annealing is conducted at about 600xc2x0 C. for several hours to ten several hours so that nickel and other impurities are removably attracted to phosphorus. At a temperature of 600xc2x0 C., this method utilizes a property that nickel is remarkably moved although phosphorus hardly moves in the film.
Although a sufficient effect is obtained even by the above method, a long period of time is required for processing. Also, an area of the region where phosphorus is added is required to increase, thereby leading to a problem that the fining of a circuit is adversely affected by such requirement, or the like. In particular, the gettering technique that imposes restrictions on the fining of the circuit goes against an advance in technique.
The present invention has been made to eliminate the above problems. The present inventors have found that phosphorus is activated, thereby being capable of significantly saving the processing period of time.
Also, the present inventors have found that an area of the region where phosphorus is added is greatly reduced. The activating was carried out by the laser technique and the RTA (a short-period heat treatment by irradiation of infrared rays) technique, as a result of which both of those techniques were effective.
FIGS. 1A to 1C are graphs showing the results obtained by adding phosphorus in the form of stripes to a silicon film which is crystallized by nickel, and investigating a gettering capacity with a change in a heating period, an area of a region where phosphorus is added (defined by a width S xcexcm of the stripes in FIGS. 1A to 1C) and an area of a region where no phosphorus is added (defined by a width L xcexcm of the stripes in FIGS. 1A to 1C). In the figures, what are indicated by a mark xcex94 are results obtained by activating phosphorus through laser before the heat treatment.
The above investigation was made under the condition where a heating temperature was 600xc2x0 C., and the dose of phosphorus was 5xc3x971014 ions/cm2. As a result, the area of the region where minimum phosphorus required for the completion of gettering is added (defined by the width S xcexcm of the stripes in FIGS. 1A to 1C) is graphed with a change in the area of the region where no phosphorus is added (defined by the width L xcexcm of the stripes in FIGS. 1A to 1C) and the heating period. FIG. 1A shows the results when the heating period is 4 hours, FIG. 1B shows the results when the heating period is 8 hours, and FIG. 1C shows the results when the heating period is 12 hours.
As is apparent from FIGS. 1A to 1C a method in which a heat treatment is conducted after phosphorus is activated through laser is higher in gettering capacity. In other words, it is clearly found that the film which has been subjected to laser processing can be more shortened in processing period and more reduced in a phosphorus-doped region area.
FIGS. 2A and 2B are photographs visually showing an appearance where nickel is subjected to gettering. When nickel is in a silicon film, portions of the silicon film where nickel is contained have a property that it is liable to be etched by a solution called as xe2x80x9cFPMxe2x80x9d so as to be pierced for a short period of time. Utilizing such a property, an appearance that nickel is gettered was photographed.
In the figures, numberless black points are portions where nickel exists. FIG. 2A shows a state of the film before gettering, and FIG. 2B shows a state of the film after gettering.
An appearance that nickel disappears from some region is well found from those photographs. The concentration of metal elements in a region which has been completely subjected to gettering was 5xc3x971016 ATOMS/cm3 or less.
Hereinafter, the reason why the efficiency of gettering is enhanced when phosphorus is activated will be considered. Since phosphorus moves along grain boundaries in a semiconductor film at the time of heating, a large energy is required for the movement. On the other hand, since nickel is moved in clearances between atoms, it can move relatively easily. In this situation, when phosphorus is in an inactive state, it relatively easily reaches the grain boundaries and slightly moves. However, when phosphorus is in an active state, a heat of 1000xc2x0 C. or higher is required in order to disconnect its bond so that phosphorus moves along the grain boundaries. This is because the grain boundaries are hardened by an energy that allows phosphorus to be activated, and a path of phosphorus is partially interrupted. Hence, the activation is effective means for fixing phosphorus.
Also, if phosphorus is activated, the gettering capacity is enhanced by its electric force. On the other hand, since upon reception of an energy produced when phosphorus is activated, nickel is diffused into the film as nickel silicide, there comes to a state where the film is liable to be more gettered.
It can be expected from the above consideration it is improper to conduct gettering at a temperature of 1000xc2x0 C. or higher. A temperature suitable for gettering was about 950xc2x0 C. at maximum.
Also, although the same effect as that when the simple substance of nickel is used is not obtained, one or plural kinds of catalytic elements selected from Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au can be employed as other crystallization promoting catalytic elements. Also, Ni may be added to those element group and used together with other metal.
Further, although the same effect as that when the simple substance of nickel is used is not obtained, one or plural kinds of catalytic elements selected from Ge, Pb and In can be used as other crystallization promoting catalytic elements.
Compared with the above element group of Ni, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au, the element group of Ge, Pb and In is slow to the degree of 1/100 in in-film diffusion speed at the same temperature, and therefore gettering must be conducted at a relative high temperature.
As elements that enable the above crystallization promoting catalytic elements to be gettered, there have been known 15-group elements such as N, As, Sb or Bi other than phosphorus. In the present specification, those elements including phosphorus are called xe2x80x9cgettering elementsxe2x80x9d. Those elements may be used instead of or together with phosphorus. Otherwise, plural kinds of elements may be used together. However, the use of phosphorus is most effective.
Since phosphorus or the like can be used as n-type dopant, after phosphorus is introduced into the source and drain regions of a TFT having an active layer containing nickel therein, and the source-drain region is then activated by laser or the like, thermal annealing at about 600xc2x0 C. is conducted on the layer. As a result, there occurs a phenomenon that phosphorus allows nickel to be sucked out from the channel region and the high-resistant region of the TFT, that is, gettering. With this phenomenon, impurities such as nickel can be removed from the channel region or high-resistant region of the TFT. The characteristic of the TFT is hardly adversely affected by nickel so far as nickel is in the source and drain regions.
Although only a TFT of an N channel is manufactured by this method, a TFT of a P channel can be also manufactured with addition of p-type dopant such as phosphorus. Also, in this case, the gettering capacity of phosphorus is not changed. There exists substantially no Ni-Six in the depletion layer of n-i and p-i junctions of the TFT manufactured in the above method.
The present invention has been initially devised for a low-temperature process, but is also effective when the same process is conducted on a semiconductor device formed on a quartz substrate that can be subjected to a higher-temperature process than 600xc2x0 C., for example, the application of a temperature of 850xc2x0 C. or higher. The effect is to remove Ni in the film having higher crystallinity which has been obtained by Ni in a relatively short period of time. Also, an area of the region to which gettering elements are added can be reduced more than the conventional one.
From the above viewpoints, the invention is summarized by a technique in which after the gettering elements are sufficiently activated in a semiconductor film, the semiconductor film is heated at a temperature lower than a temperature required for the former activation, to thereby getter impurities in the semiconductor film efficiently.
According to a first aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising:
a first step of forming an amorphous semiconductor film containing silicon therein on a substrate having an insulating surface;
a second step of introducing catalytic elements that promote the crystallization of the amorphous semiconductor film into the amorphous semiconductor film;
a third step of crystallizing the amorphous semiconductor film through a heat treatment;
a fourth step of selectively introducing elements that enable the catalytic elements to be gettered into a semiconductor film obtained in the third step;
a fifth step of activating the gettering elements; and
a sixth step of gettering the catalytic elements through a heat treatment in a region into which the gettering elements are introduced in the fourth step;
wherein the third and sixth steps are conducted so that a temperature of the substrate does not exceed a strain point temperature of the substrate.
The use of a laser is proper for the activation according to the first aspect of the present invention.
The use of RTA is proper for the activation according to the first aspect of the present invention.
The RTA is means for heating and annealing a region to which an intense light is irradiated. The intense light to be generally used is infrared rays.
The catalytic elements that promote the crystallization according to the first aspect of the present invention may be one or plural kinds of elements selected from Ni, Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au.
The catalytic elements that promote the crystallization according to the first aspect of the present invention may be one or plural kinds of elements selected from Ge, Pb and In.
As elements that can getter the above crystallization promoting catalytic elements, there have been known 15-group elements such as N, As, Sb or Bi other than phosphorus, and any elements exhibit the effects of the present invention.
According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising:
a first step of forming an amorphous semiconductor film containing silicon therein on a substrate having an insulating surface;
a second step of introducing nickel which is a catalytic element that promotes the crystallization of the amorphous semiconductor film into the amorphous semiconductor film;
a third step of crystallizing the amorphous semiconductor film through a heat treatment;
a fourth step of selectively introducing phosphorus which is an element that can getter the catalytic element into the semiconductor film obtained in the third step;
a fifth step of activating phosphorus which is the gettering element; and
a sixth step of gettering nickel which is the catalytic element through a heat treatment in a region into which phosphorus which is the gettering element is introduced in the fourth step;
wherein the third and sixth steps are conducted so that a temperature of the substrate does not exceed a strain point temperature of the substrate.
The use of a laser is proper for the activation according to the second aspect of the present invention.
The use of RTA is proper for the activation according to the second aspect of the present invention.
In the fifth step according to the second aspect of the present invention, it is effective that a sheet resistance of the region in which phosphorus is activated is 10 Kxcexa9/xe2x96xa1 or less.
In the fifth step according to the second aspect of the present invention, it is more effective that a sheet resistance of the region in which phosphorus is activated is 3 Kxcexa9/xe2x96xa1 or less.
In the fourth step according to the second aspect of the present invention, it is very effective that a rate of the area of the region in which phosphorus is added to an area of the region in which nickel is gettered is even in a range of from 0.05 to 0.6.
In the fourth step according to the second aspect of the present invention, it is effective that the rate of the area of the region in which phosphorus is added to the area of the region in which nickel is gettered is even in a range of from 0.1 to 0.5.
In the fourth step according to the second aspect of the present invention, it is effective that the amount of adding phosphorus is in a range of from 1xc3x971013 to 1xc3x971016 IONS/cm2.
In the fourth step according to the second aspect of the present invention, it is effective that the amount of adding phosphorus is in a range of from 1xc3x971014 to 3xc3x971015 IONS/cm2.
In the third and sixth steps according to the second aspect of the present invention, it is effective that a thermal annealing temperature is 400 to 850xc2x0 C.
In the third and sixth steps according to the second aspect of the present invention, it is more effective that the thermal annealing temperature is 500 to 750xc2x0 C.
In the sixth step according to the second aspect of the present invention, it is effective that the thermal annealing period is 1 minute to 20 hours. In the sixth step according to the second aspect of the present invention, it is more effective that the thermal annealing period is 30 minute to 3 hours.
In the fourth step according to the first or second aspect of the present invention, the present invention is effective when no gettering element is added to a region in which the device is formed.
In the fourth step according to the first or second aspect of the present invention, the present invention is effective when no gettering element is added to both of a channel region and a high-resistant region (offset region) of the device.
Another structure of the present invention is a semiconductor device in which nickel is added to source and drain portions, and there exists substantially no Ni-Six in a depletion layer of the n-i and p-i junctions.
The above and other objects and features of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings.